The present invention relates to an image processing circuit and an image processing method, and more particularly, to a circuit and method for correcting pixel defects included in color image data.
Solid state imaging devices, such as a CCD, are nowadays often used. A solid state device includes a matrix of pixels that receive light. Each pixel (i.e., sub-pixel) receives red (R), green (G), and blue (B) light and generates image data. The image data of the pixels configures color image data. The pixels of a solid-state imaging device may include structural defects due to factors resulting from the manufacturing process. Thus, the image data generated by a pixel having a defect must be corrected with the image data generated by pixels located in the proximity of that defective pixel.
A first prior art example of a solid state imaging device that generates color image data includes a filtering portion and an imaging portion. The filtering portion is formed by arranging one red filter (R), two green filters (Gr and Gb), and one blue filter (B) in a Bayer array. The imaging portion includes a plurality of light receiving elements for receiving the light that passes through each filter. Each light receiving element functions as a sub-pixel. Each pixel forming the color image data includes four filters and four light receiving elements. The color image data for each pixel is configured by the data for four colors (R, Gr, Gb, and B).
The light receiving elements included in a solid state imaging device may include structural defects resulting from the manufacturing process. For example, the data amount corresponding to the amount of received light, or the so-called photoelectric conversion efficiency, for a certain light receiving element may differ from that of the other light receiving elements. As a result, the data for some of the four colors in the image data for that light receiving element may differ from the actual color of the image subject. An image processing circuit compares the data value for each color in the image data generated by the solid state imaging device with a threshold value to check for defects in each light receiving element. When a defect is found, the image processing circuit corrects the color data generated by the defective light receiving element.
In the solid state imaging device of the first prior art example, a single pixel is formed by four light receiving elements laid out on the same plane. Accordingly, the incident light amount in each light receiving element is one fourth of that of a single pixel. Thus, each light receiving element can use only one fourth of the light irradiating a single pixel region. Further, each light receiving element receives the light that passes through the corresponding filter in the Bayer array. Therefore, the red color light and blue color light are received in alternate lines and the light for each color is received by every other pixel. This widens the intervals between the light receiving elements for each color. As a result, it is difficult to increase the resolution.
Accordingly, in a second prior art example of a solid state imaging device, light receiving elements are laid out in a direction perpendicular to a light receiving plane. In the second prior art example, the light entering a semiconductor substrate proceeds until reaching a depth corresponding to the wavelength of the light. For example, when three light receiving elements are superimposed in the direction perpendicular to the light receiving plane, each of the three light receiving elements converts the light of the wavelength corresponding to the location of that light receiving element into an electric signal. The light receiving area of each light receiving element is the same as the area of a single pixel. Accordingly, each light receiving element converts all of the light entering the pixel into electric signals. Thus, the usage rate of the incident light amount is high compared to the first prior art example, and the data amount increases. Further, the light receiving elements for each color are arranged adjacent to one another. This enables the resolution to be increased.